4. Climate Change and Hydrological Responses in Himalayan Basins, Nepal

Studies on water and related fields are vital for protecting the environment and climate. Lack of hydrometeorological data, particularly in a high-altitude region such as Nepal, hinders the process of understanding the systems of earth science dynamics. In this study, observed data were used for the period 1988–2010 from three high-altitude regions, viz., Annapurna, Langtang, and Khumbu, of Nepal. The Coupled Global Climate Model (CGCM3) for A1B SRES scenarios during the period 2001–2060 was used to determine projections. The statistical downscaling model (SDSM) was used to downscale precipitation and temperature data at the Modi, Langtang, and Dudh Koshi river basins. The simulated precipitation and temperature data were corrected for bias before implementation in the conceptual rainfall–runoff model Hydraologiska Byrans Vattenbalansavde (HBV) for hydrological response analysis. In the HVB-light 3.0, the Groups Algorithms Programming (GAP) optimization approach and calibration were used to obtain several parameter sets that were ultimately reproduced to observe the stream flow.

The CGCM3 model projects increasing trends in annual as well as seasonal precipitation, except in summer [June, July August, September (JJAS], during 2001–2060 for A1B SERS emission scenarios over the three sites under investigation. The model projects warmer days in every season of the entire period from 2001 to 2060. These warming trends are higher in maximum than in minimum temperatures throughout the year, which indicates an increasing trend of daily temperature range as the greenhouse effect increases. Further, trends for post-monsoon (ON) temperature are much cooler compared to the remaining three seasons (months) over all three sites. In addition, decreasing trends in summer discharge at Langtang Khola and increasing trends in Modi Khola and Dudh Koshi river basins are evident. Among all basins, the flow regime is more pronounced during the later parts of future decades as compared to the preceding decades.